As herein and elsewhere disclosed, a strain of aerobic bacteria has been isolated which encapsulate themselves, from which a bio-polymer can be extracted. Neutralization of the alkaline extract with mineral acids, organic acids or CO.sub.2 results in gel formation. Polymer in hydrated gel is resistant (and tolerant) to repeated cycles of redissolving in alkali followed by precipitation by acid or CO.sub.2. The subject invention sets forth the feasibility and methods of using this microbial polymer for permeability modification and reversible blocking of undesirable flow channels in petroleum sands, horizons and reservoirs.
Most of the Kansas, for example, and many elsewhere, oil reservoirs have already been water flooded in secondary recovery. The water/oil ratio in most of them has already reached or passed the economic level. Therefore, devising and providing a technique which will selectively and reversibly plug the water channels has great economic prospects. Our invention establishes that the bio-polymer has potential for application in microbially enhanced oil recovery (EOR). The potential and capacity for generating the reversibly gellable (in situ) polymer from inexpensive, renewable cellulosic, hemicellulosic or cornstarch stocks greatly enhances the economic feasibility and usefulness of the subject process.
Permeability modification has been a subject of interest since the introduction of water-flooding as a secondary oil recovery technique. Because of the inevitable variations in the reservoir's permeability, bypassing of the displaced fluid by the displacing fluid is unavoidable even in the most homogeneous reservoir. Early breakthrough of the displacing fluid causes the secondary recovery (typically water drive) project to become uneconomical and leaves a large portion of the initially present oil in place behind and unrecovered.
Several processes such as injection of polymer solution (1) or cross linking of polymers (2) in situ in the reservoir (in situ gelation) have been developed and are presently under investigation. The difficulty arises when deep penetration is required. Near well-bore treatment is easier to achieve than treatments requiring deep penetration of the reservoir.
Clearly, it is desirable to devise a method and/or process which is time independent and reversible. In such case, materials could be injected as far in the reservoir as desired, then be activated to gel. Process reversibility would allow breaking the first in situ gel, moving it further down in (through) the reservoir and then repeating the gelation process again. One objective of the subject method and process is to disclose and provide the feasibility of such a technique using a reversible gel generated by a bio-organism.
The in situ growth of anaerobic and/or aerobic bacteria and the accumulation of the products of their growth have been considered for use in enhanced oil recovery (EOR) processes (3). Products of anaerobic bacterial growth which may enhance flow characteristics of in situ oil include gases such as carbon dioxide and methane, solvents such as ethanol or butanol, and acetic, propionic, or butyric acid. Potentially useful products of aerobic bacteria growth include surfactants (4) produced by hydrocarbon oxidizing bacteria and polysaccharide gums (5) which increase the viscosity of water.
In addition to problems attendant to the creation of environments suitable for the in situ growth of bacteria, the biomass may eventually accumulate in amounts sufficient to cause clogging. Problems involved in the in situ use of bacteria may be contrasted with the relative ease with which desirable microbial products can be produced in large scale cultures. Such products can then be injected into the wells. One such product is xanthan, a polysaccharide polymer which is injected into wells in order to increase the viscosity of water (5).
The subject method and process demonstrates and discloses the feasibility of using microbial polymers capable of gel formation for reversible blocking of undesirable channels. It focuses on bacterial polymers which can reversibly form gels. Such particular polymers can readily be obtained from a certain newly isolated strain of cellulolytic bacteria as well as some such bacteria previously known and further some unrelated bacteria as set forth herebelow.